This invention relates to novel spiro carboxylic acids and their insecticidal esters, as well as insecticidal compositions containing said esters as an essential active ingredient.
Current trends in the chemical control of insects call for inherently safer materials which degrade very rapidly to non-toxic substances once their purpose is accomplished. The safety of the widely used chlorinated hydrocarbons, notably DDT, is currently under question largely because of their poor biodegradability and concomitant persistence. Accordingly, there is a great demand for alternative broad spectrum insecticides which are suitable for the high volume usage entailed in agricultural applications. At the same time it is desirable for new insecticides to exhibit a low order of toxicity to warm-blooded animals. Of the several insecticide classes which demonstrate low mammalian toxicity and good biodegradability, it has long been recognized that pyrethrum, a naturally-occurring insecticidal mixture, possesses these desirable properties. In addition to the safety advantages, this natural mixture causes rapid knockdown and kill of a broad spectrum of insects; however, it is unstable to light, air, and heat, and is very expensive. The most active component of pyrethrum is pyrethrin I and a number of analogous compounds have been proposed for insecticidal use. Allethrin, a typical synthetic pyrethrin-like insecticide, while more stable to light and heat than pyrethrum, is nevertheless expensive, a defect which is compounded by the fact that this substance is not appreciably synergized by the low cost synergizing agents such as piperonyl butoxide which are typically used in insecticidal compositions. Because of instability, high cost and limited supply, the use of pyrethrum and pyrethrin-like insecticides in agricultural applications has been precluded or seriously limited.
At the same time, it is well known that certain insects, in time, become immune to the insecticidal properties of various chemical agents. To be efficient, an insecticide should be able to resist detoxification by the insect. The biological mechanisms whereby insects are capable of detoxifying the various types of insecticidal compounds are not known. However, it has been suggested that with compounds which are analogous to pyrethrin, e.g., allethrin, one mode of detoxification may involve oxidation of one or both of the methyl groups on the isobut-1-enyl side chain of the chrysanthemic acid moiety present in that compound. Additionally, it is possible that, as with other biological systems, insects may in time develop new biogenetic mechanisms capable of detoxifying any particular insecticidal compound. In any event, it is desirable to have included in the insecticidal armamentarium compounds which may be utilized once a given class of insects is found no longer to respond to conventional insecticidal compounds.
Many prior art insecticidal esters differ from one another and from the natural pyrethrin I esters by virtue of synthetic modifications in the alcohol moiety of the ester. Other synthetic insecticides are pyrethrin-like esters modified in the acid portion of the ester molecule. British specification No. 1,207,371, Sept. 3, 1970, relates to the allethrolone esters of the spiro carboxylic acids 2-(isobut-1' -enyl)spiro[2.5]octane-1-carboxylic acid and 2-(isobut-1' -enyl)spiro[2.4]heptane-1-carboxylic acid. French Patent No. 1,505,423, December, 1967, relates to the ethyl and allethrolone esters of 2,2,5-trimethylspiro[ 2.5]oct-4-ene-1-carboxylic acid. By the present invention, certain novel spiro carboxylic acids are provided which, when esterified with various alcohols, form insecticidal analogues of pyrethrin which are modified in the acid moiety of the ester. Suprisingly, the allethrolone esters of the acids herein exhibit miticidal activity, a property not shared by many other pyrethrin-like compounds.
It is therefore an object of this invention to provide novel spiro carboxylic acids which can be esterified to provide a variety of insecticidal compounds which are biodegradable, effect rapid knock-down and kill of a broad spectrum of insects (the term "insects" herein includes mites, and the term "insecticidal" includes miticidal) possess low mammalian toxicity, and are less susceptible to detoxification by insects than is pyrethrum. It is a further object of this invention to provide certain insecticidal allethrolone esters of novel spiro carboxylic acids. These and other objects are obtained by the present invention as will become apparent from the following disclosure.